As I understand it, you can make a backup in iTunes and restore it to a second device. This will give you two devices that both think they own their client ID. We might need to somehow hash a device ID, exclude the client ID from backups, or some other solution to make this better. It's worth noting that sometimes this is desirable -- e.g., when replacing a device. Oh, for proper device management. There might be similar consequences for FxA certs and issued tokens.

Apple has made some provision for these situations that I intend to use for Account storage (although I'm not sure we do yet). See [1]. Specifically, Account stuff (email, uid, service endpoints) will be kSecAttrAccessibleAlways and State stuff (session tokens, oauth tokens, certificates, etc) will be kSecAttrAccessibleAlwaysThisDeviceOnly. (I see no reason to have to unlock the device first, etc.) [1] https://developer.apple.com/library/ios/documentation/Security/Reference/keychainservices/#//apple_ref/doc/constant_group/Keychain_Item_Accessibility_Constants

The User Defaults system has a similar concept, but it's only accessible through CFPreferences: https://developer.apple.com/library/mac/documentation/CoreFoundation/Reference/CFPreferencesUtils/#//apple_ref/doc/constant_group/Application_Host_and_User_Keys There's a hacky way or two to detect restore: http://stackoverflow.com/a/19979849/22003 http://stackoverflow.com/a/26059085/22003 http://stackoverflow.com/questions/18868576/udid-replacement-in-ios7/18868671#18868671

I just restored a phone backup to a new iPad. Firefox appeared. As expected, it's not signed in to sync. But it had my open tabs and my history. That means that: * The clients and commands tables are cloned from my phone. * Potentially the client ID is the same. * History local/remote bit is wrong. * If we add source device to history (Bug 1302797), it'll be wrong, too.

Tracking nom to think about this in the context of overall sync reliability. Firefox has been out for long enough now that users will be upgrading and buying second devices, and multiple devices is the value prop for Sync.